Does anyone know for sure, that it will damage or wreck the motor in a 400ex if you straight pipe it?

 

you need a certain amount of back pressure for an engine to work properly. besides , just cause its loud doesnt mean its fast.

 

very correct plus why would you want to run straight pipe?

 

i raced a strait piped yfz at sand mntn. and it was nothing more than loud.[img]i/expressions/face-icon-small-wink.gif[/img]

 

I'm going to play the devil's advocate.

Go ask Dale Earnhardt if he'd run a muffler on his race car.

Same principal. I think tuning the head pipe and jetting would be the key though. Maybe the intake since all three work together. Might lose some low end.

 

My HMF is Basicly a straight pipe and it really opened it up from stock

 

how can a 600 hp v8 be compared to a 25 hp single cylinder motor .just the amount of flow required to make that motor run is probably enough to suck start a harley. it needs the most free flowing exaust out there, but dont think because there's no "muffler" that there is no back pressure in the pipes, thier bent and cut to whatever length for that . if the had monster blowers they could run 2 foot pipes. after that much hp exhaust no longer matters so long as it gets the heat away from the motor and flows as much as it takes in.

 

A headpipe will provide all the backpressure you need if it is the right length and diameter. All a baffle will do is distort the airflow and hinder performance.

 

Does anyone know what size pipe I should use? Would stock size be alrigh?

 

ill bet that motor does'nt last a year. even drag quads run expansion chambers and "mufflers". how many has anyone seen not running any sort of backpressure causing devise.